CANDIDATE- Dr. Thomas Robinson, MD is an Associate Professor of Surgery at the University of Colorado at Denver (UCD). Dr. Robinson has a strong background in both aging related research (studying post-operative delirium) and education (teaching surgeons geriatric specialty knowledge). Dr. Robinson's immediate career goals are to learn the skills necessary to perform exceptional aging-related translational research in the field of surgery. Dr. Robinson's long term career goals are to become an independent translational researcher with a focus on studying post-operative delirium in elderly patients, and to become a national champion of geriatrics research and education within the field of surgery. RESEARCH PROJECT- Post-operative delirium is a common, deleterious complication in elderly patients. This double-blinded, placebo controlled trial (including subjects 60 years and older following a major operation requiring surgical ICU admission) will randomize patients to receive L-tryptophan supplementation or placebo with the primary outcome measure being the incidence and/or duration of excitatory (both hyperactive and mixed) post-operative delirium. Delirium will be assessed twice daily post-operatively. Biomarkers (tryptophan, serotonin and melatonin) will be measured pre- and post-operatively. We hypothesize that the incidence and/or duration of excitatory (both hyperactive and mixed) post-operative delirium will be reduced in the group receiving L-tryptophan supplementation compared to placebo. CAREER DEVELOPMENT- The three main areas of Dr. Robinson's career development plan includes clinical research knowledge, geriatric specialty care knowledge and neuropsychology knowledge. At the end of the career development training, Dr. Robinson will be a surgeon who has acquired the skills of a translational research, and who understands fundamentals in geriatrics and the neurosciences. ENVIRONMENT- The environment at UCD is ideal for allowing an enthusiastic young surgeon to acquire expertise and to perform surgical aging-related translational research. The Department of Surgery resolutely supports Dr. Robinson's research and career development efforts. Dr. Robinson has established close and productive mentor-mentee relationships over the past two years with his primary co-mentors. The Denver VA supports enrollment of geriatric surgical patients for the proposed study.